We propose extension and development of our past research on the C-H acidities of various organic compounds. Carbanions are among the most important intermediates and proton transfer is one of the most important reactions in organic and biochemical processes. Our goal in this study is fundamental knowledge of the effect of structural changes on carbanion stability and of the role of solvent and ion-pairs in proton transfer reaction mechanisms. Experimental methods include spectroscopic determination of equilibrium acidities and base-catalzyed hydrogen isotope exchange kinetics of various carbon acids: aromatic hydrocarbons, saturated and unsaturated alkanes and cycloalkanes, sulfur-, phosphorus-, silicon- and other substituted systems. The studies of reaction mechanism include substitutent effects, primary and secondary isotope effects and Bronsted correlations. A complementary theoretical study includes ab initio calculations of suitable model systems.